[MercadoLibre] Add extractor

[alveardevs]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Added support for downloading short videos from products offered at MercadoLibre.com.ar
That's the main e-commerce from Argentina

Fixes #

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[alveardevs]

Note : All tests passed before commit but might be failing soon due to :

• The high inflation rate in this country (AR) so the 'price' field will probably differ to the one we set in the tests.
• The product to be tested could no longer be available to be bought.